The chapter "Reliability of Power in Physical Performance Tests" by Will G. Hopkins, Elske J. Schabort, and John A. Hawley reviews the reliability of power measures in physical performance tests. The authors meta-analyzed 101 studies to identify the most reliable measures and factors affecting reliability. Key measures of reliability include the standard deviation of individual difference scores, ANOVA, retest correlation coefficients, and mean intraindividual standard deviations. The most reliable tests for power or work include field tests of sprint running, peak power in incremental tests, constant-power tests, lactate-threshold power, and jump height or distance. Factors affecting reliability include test type, athletic status, gender, test duration, inter-trial time, and test-specific factors. The importance of practice trials was highlighted, with the CV between the first two trials being 1.3 times higher than subsequent trials. The findings aim to guide exercise practitioners and researchers in selecting or designing reliable tests for physical performance assessments.The chapter "Reliability of Power in Physical Performance Tests" by Will G. Hopkins, Elske J. Schabort, and John A. Hawley reviews the reliability of power measures in physical performance tests. The authors meta-analyzed 101 studies to identify the most reliable measures and factors affecting reliability. Key measures of reliability include the standard deviation of individual difference scores, ANOVA, retest correlation coefficients, and mean intraindividual standard deviations. The most reliable tests for power or work include field tests of sprint running, peak power in incremental tests, constant-power tests, lactate-threshold power, and jump height or distance. Factors affecting reliability include test type, athletic status, gender, test duration, inter-trial time, and test-specific factors. The importance of practice trials was highlighted, with the CV between the first two trials being 1.3 times higher than subsequent trials. The findings aim to guide exercise practitioners and researchers in selecting or designing reliable tests for physical performance assessments.